The well‐known Fraunhofer approximation provides a simple and direct qualitative physical explanation for the diffraction oscillations and the oscillation phase shift phenomena observed in differential rotational state to state scattering cross sections for He on a number of small molecules. This approximation has been further developed to yield a simple analytical expression for the angular dependence of the inelastic cross sections. For the experimentally and theoretically well investigated systems He–N2 and He–CH4 the Fraunhofer formula is found to reproduce the measured cross sections to within better than a factor of 2. For the investigated collision energy Ecm ≊30 meV (≊3 kJ/mol) the deformed sphere interaction potential model used in the Fraunhofer approximation appears to be closely related to the zero crossing equipotential line of the full interaction potential. The relationship to the cluster model of molecules composed of atomic hard spheres is discussed. The dependence of the rotational excitation on the interaction potential is shown to be primarily a dependence on the equilibrium positions of the atoms in the molecule.

1.
S. I.
Drozdov
,
JETP
28
,
734
(
1955
)
[translation:
Soviet Physics JETP
1
,
791
(
1955
)].
2.
J. S. Blair, in Nuclear Structure Physics, edited by P. D. Kunz et al. (The University of Colorado, Boulder, 1966), Vol. VIIC, p. 343–444 (in particular p. 344–351 and 385–409).
3.
M.
Faubel
,
K. H.
Kohl
,
J. P.
Toennies
,
K. T.
Tang
, and
Y. Y.
Yung
,
Faraday Discuss. Chem. Soc.
73
,
205
(
1982
).
4.
M.
Faubel
,
Adv. At. Mol. Phys.
19
,
345
(
1983
).
5.
P.
Habitz
,
K. T.
Tang
, and
J. P.
Toennies
,
Chem. Phys. Lett.
85
,
461
(
1981
).
6.
M. Born and E. Wolf, Principles of Optics, 6th ed. (Pergamon, Oxford, 1980), pp. 382–383, 392–401, and 414–417.
7.
D. J. Kouri, in Atom‐Molecule Collisions, edited by R. B. Bernstein (Plenum, New York, 1979), pp. 301–358.
8.
G. A.
Parker
and
R. T.
Pack
,
J. Chem. Phys.
68
,
1585
(
1978
).
9.
K. H. Kohl, Ph.D. thesis, University of Gottingen, 1982. Max‐Planck‐Institut für Strömungsforschung, Göttingen, Bericht 17/1982.
10.
M. Faubel, K. H. Kohl, and J. P. Toennies, in Physics of Electronic and Atomic Collisions, edited by S. Datz (Oak Ridge National Laboratory, Oak Ridge, 1981), pp. 935–936.
11.
H. S. W.
Massey
and
C. B. O.
Mohr
,
Proc. R. Soc. London Ser. A
141
,
434
(
1933
).
12.
N. F. Mott and H. S. W. Massey, The Theory of A tomic Collisions (Clarendon, Oxford, 1971), pp. 38–40.
13.
M. A. D. Fluendy and K. P. Lawley, Chemical Applications of Molecular Beam Scattering (Chapman and Hall, London, 1973), pp. 212–216.
14.
A. R. Edmonds, Angular Momentum in Quantum Mechanics (Princeton University, Princeton, 1960).
15.
S.
Green
,
J. Chem. Phys.
64
,
3463
(
1976
).
16.
D. Secrest, in Atom‐Molecule Collision Theory, edited by R. B. Bernstein (Plenum, New York, 1979), pp. 265–299.
17.
L. N.
Smith
,
D. J.
Malik
, and
D.
Secrest
,
J. Chem. Phys.
71
,
4502
(
1979
).
18.
L. N.
Smith
and
D.
Secrest
,
J. Chem. Phys.
74
,
3882
(
1981
).
19.
B.
Schramm
,
Faraday Discuss. Chem. Soc.
73
,
283
(
1982
);
R. R.
Fuchs
,
Faraday Discuss. Chem. Soc.
73
,
285
(
1982
).,
Faraday Discuss. Chem. Soc.
20.
M.
Faubel
,
K. H.
Kohl
,
J. P.
Toennies
, and
F. A.
Gianturco
,
J. Chem. Phys.
78
,
5629
(
1983
).
21.
F.
Battaglia
,
F. A.
Gianturco
, and
A.
Palma
,
J. Chem. Phys.
80
,
4997
(
1984
).
22.
V. Staemmler and U. Buck (private communciation).
23.
H. A. Stuart, Molekülstruktur (Springer, Berlin, 1967), pp. 84, 95.
24.
T. Kihara, Intermolecular Forces (Wiley, Chichester, 1979), pp. 90, 91.
25.
J. O.
Hirschfelder
,
R. B.
Bird
, and
E. L.
Spotz
,
J. Chem. Phys.
16
,
968
(
1948
).
26.
(a)
R. T.
Pack
,
Chem. Phys. Lett.
55
,
197
(
1978
);
(b)
G. A.
Parker
,
M.
Keil
, and
A.
Kuppermann
,
J. Chem. Phys.
78
,
1145
(
1983
).
27.
V.
Khare
,
D. E.
Fitz
, and
D. J.
Kouri
,
J. Chem. Phys.
73
,
2802
(
1980
).
28.
D.
Beck
,
U.
Ross
, and
W.
Schepper
,
Phys. Rev. A
19
,
2173
(
1979
).
29.
R. Schinke and J. M. Bowman, in Molecular Collision Dynamics, edited by J. M. Bowman (Springer, Berlin, 1983), pp. 61–115.
This content is only available via PDF.
You do not currently have access to this content.